Modelling of Landfill Gas Adsorption with Bottom Ash for Utilization of Renewable Energy Dissertation submitted to the Department of Civil Engineer, University of Duisburg-Essen for the degree of “Doktor-Ingenieur” (Dr.-Ing.) by Chen Miao born on January 5, 1979 in Jiangsu, P.R. China Date of examination: 06 October 2011 Reviewer: Prof. Dr.-Ing. Renatus Widmann Prof. Dr.-Ing. Tim Ricken Preface and Acknowledgement This work is carried out at the ‘Abteilung Siedlungswasser- und Abfallwirtschaft’ of Faculty of Engineering in Duisburg-Essen University in close cooperation with the ‘Lehrstuhl Mechanik- Statik-Dynamick’ of Faculty of Architecture and Civil Engineering in TU Dortmund. I am heartily grateful to my doctoral supervisor Professor Renatus Widmann for supporting me in terms of development of my scientific and professional skills through my study in Univer- sity of Duisburg-Essen. I particularly thank the supervisor Professor Tim Ricken of Faculty of Architecture and Civil Engineering in TU Dortmund. He gives me great support in modelling development. This work could never be realized without the opportunity offered by Professor J.-D. Herbell at Institute of Waste Technology of Duisburg-Essen University, that is my first chance to study abroad in life. I am thankful for the support of the China Scholarship Council. As a beneficiary of ‘State-Sponsored Graduate Scholarship Program for Building High-level Universities’, I am able to give undivided attention to scientific research. Many thanks belong to my colleagues and every one who gives me advice and help. I particularly thank Mr. Serdar Serdas and Mr. Daniel Werner. Their warm and friendly cooperation touches me deeply. I wish to extend to my personal thanks: To my beloved family. Thanks for my parents’ great support, their encouragement gives me intense confidence and passion in study through these years. I also owe my sincere gratitude to my friends. They give me their time in listening to me and accompanying me patiently during the difficult course of the thesis. Chen Miao Duisburg, Germany August 2011 Summary I Summary Energy crisis, environment pollution and climate change are the serious challenges to people worldwide. In the 21st century, human being is trend to research new technology of renewable energy, so as to slow down global warming and develop society in an environmentally sustain- able method. Landfill gas, produced by biodegradable municipal solid waste in landfill, is a renewable energy source. In this work, landfill gas utilization for energy generation is introduced. Landfill gas is able to produce hydrogen by steam reforming reactions. There is a steam reformer equipment in the fuel cells system. A sewage plant of Cologne in Germany has run the Phosphoric Acid Fuel Cells power station with biogas for more than 50,000 hours successfully. Landfill gas thus may be used as fuel for electricity generation via fuel cells system. For the purpose of explaining the possibility of landfill gas utilization via fuel cells, the thermodynamics of landfill gas steam reforming are discussed by simulations. In practice, the methane-riched gas can be obtained by landfill gas purification and upgrading. This work investigate a new method for upgrading-landfill gas adsorption with bottom ash ex- perimentally. Bottom ash is a by-product of municipal solid waste incineration, some of its physical and chemical properties are analysed in this work. The landfill gas adsorption experi- mental data show bottom ash can be used as a potential adsorbent for landfill gas adsorption to remove CO2. In addition, the alkalinity of bottom ash eluate can be reduced in these adsorption processes. Therefore, the interactions between landfill gas and bottom ash can be explained by series reactions accordingly. Furthermore, a conceptual model involving landfill gas adsorption with bottom ash is developed. In this thesis, the parameters of landfill gas adsorption equilibrium equations can be obtained by fitting experimental data. On the other hand, these functions can be deduced with theoretical approach. In this thesis, both of them are discussed respectively. Additionally, the diffusion phenomena of landfill gas mixtures can be expressed by Maxwell-Stefan equations and Fick’s law. According to the relation between Maxwell-Stefan equations and Fick’s law, the diffusion coefficients of landfill gas mixtures can be estimated in theory. The major part of this model is based on the theory of mass transfer through porous media. In which, mass balance, momentum balance and constitutive relations among multi-phase are employed for modeling. Landfill gas adsorption processes in two-dimension porous media can be thus simulated with application of this model. Contents III Contents List of Figures VII List of Tables IX List of Symbols and Abbreviations X 1 Introduction 1 1.1 Overview and Problem Analysis . ... 1 1.2 ScopeofThisThesis ............................... 1 2 Municipal Waste Management 3 2.1 WasteManagement................................ 3 2.1.1 Wastereduction.............................. 3 2.1.2 Recycling................................. 3 2.1.3 Composting................................ 3 2.1.4 Re-use .................................. 3 2.1.5 Energyrecovery ............................. 4 2.1.6 Landfill.................................. 4 2.2 IntegratedWasteManagement . ... 5 2.2.1 Wastegeneration ............................. 6 2.2.2 Wastepretreatmentatsource . 6 2.2.3 Collection and transport . 6 2.2.4 Processingofsolidwaste. 6 2.2.5 Transferandtransport . 6 2.2.6 Disposal ................................. 6 2.3 MunicipalSolidWaste(MSW) . 7 2.3.1 Municipal solid waste generation . ... 7 2.3.2 Municipal solid waste composition . ... 9 2.4 Municipal Solid Waste Treatment and Disposal . ........ 11 2.4.1 MSWtreatmentinEU .......................... 11 2.4.2 MSWtreatmentinGermany . 12 2.4.3 MSWtreatmentinChina. 15 3 Landfill Gas Utilization 18 3.1 LandfillGas.................................... 18 IV Contents 3.2 LandfillGasUtilization. 18 3.2.1 Overview of landfill gas utilization . ..... 18 3.2.2 Utilization of landfill gas . 19 4 Utilization of Landfill Gas for Fuel Cells 22 4.1 FuelCellComponents .............................. 22 4.1.1 Unitcells ................................. 22 4.1.2 Cellstackassembly............................ 22 4.1.3 Processingsystems............................ 23 4.2 FuelCellPerformance .............................. 25 4.2.1 TheNernstequation ........................... 25 4.2.2 Thermodynamics of a fuel cell . 25 4.2.3 PAFCanalyses .............................. 26 4.3 LandfillGasReforming.............................. 31 4.3.1 Scope on thermodynamic properties . 31 4.3.2 Steam reforming reactions . 34 4.3.3 Simulation results and discussion . 34 4.4 ConclusionandDiscussion . 38 5 Landfill Gas Adsorption with Bottom Ash 40 5.1 Municipal Solid Waste Incineration Bottom Ash . ........ 40 5.1.1 Bulk composition of bottom ash . 40 5.1.2 Chemical properties of bottom ash . 41 5.1.3 Water content and ignition loss . 43 5.1.4 Porosity and pore size distribution . ..... 44 5.1.5 Heatcapacity............................... 45 5.2 Landfill Gas Adsorption with Bottom Ash . 46 5.2.1 Fixed bed adsorption processes . 46 5.2.2 Adsorptionresults ............................ 50 5.3 Landfill Gas Adsorption Equilibrium . ...... 55 5.4 Interactions Between Landfill Gas and Bottom Ash . ...... 57 5.5 Conclusions.................................... 58 6 Diffusion Coefficients of Landfill Gas 59 6.1 Maxwell-StefanEquations . 59 6.1.1 Binarysystems .............................. 59 Contents V 6.1.2 Multicomponent systems . 59 6.2 Fick’slaw..................................... 60 6.2.1 Flux.................................... 60 6.2.2 Binarydiffusion ............................. 61 6.2.3 Multicomponent diffusion . 62 6.3 DiffusionCoefficientsinGases. 63 6.3.1 Fick and Maxwell-Stefan diffusion coefficients . ........ 63 6.3.2 Chapman-Enskog theory . 63 6.3.3 Diffusion coefficients in ternary gases system . ........ 64 6.4 Conclusions.................................... 65 7 Modelling and Simulation on Landfill Gas Adsorption 66 7.1 PhaseandPorousMedia ............................. 66 7.2 TheMassBalance................................. 67 7.3 TheMomentumBalance ............................. 69 7.4 TheEnergyBalance................................ 70 7.5 TheEntropyInequality . 71 7.6 TheChemicalPotential . 72 7.7 Governing Equations of the Calculation Concept . ....... 73 7.8 Interaction Conditions . 73 7.9 SaturationConditions. 74 7.10 LagrangeMultipliers . 75 7.11 Evaluation of Entropy Inequality . ....... 75 7.11.1 Evaluation of Lagrange multipliers . ..... 79 7.11.2 Evaluation of Cauchy stress tensors . 80 7.11.3 Evaluation of molar concentration . ..... 80 7.11.4 Evaluation of seepage velocities . ..... 81 7.11.5 Evaluation of interaction forces . ..... 81 7.12WeakForms.................................... 82 7.12.1 Momentum for mixture . 82 7.12.2 Massbalanceequations. 83 7.13 Finite Element Discretization . ....... 83 7.14 InterphaseMassTransfer . 84 7.14.1 Kineticmodels .............................. 84 7.14.2 Functions on dissipative mass exchange . ...... 85 VI Contents 7.15 Initial and Boundary Conditions . 86 7.16 SimulationResults ............................... 88 7.16.1 Concentration and chemical potential . ..... 88 7.16.2 Velocitiesoffluids . 88 7.16.3 Pressure.................................. 89 7.17 Seepagevelocity ................................ 89 7.18Convergence ................................... 92